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Abstract:

A light emitting device according to one embodiment includes: a board;
plural first light emitting units each including a first light emitting
element and a first fluorescent layer formed on the first light emitting
element having a green phosphor; plural second light emitting units each
including a second light emitting element and a second fluorescent layer
formed on the second light emitting element having a red phosphor; the
second fluorescent layers and the first fluorescent layers being
separated in a non-contact manner with gas interposed there between; and
plural third light emitting units each including a third light emitting
element and a resin layer formed on the third light emitting element
having neither a green phosphor nor the red phosphor, the third light
emitting units being disposed between the first light emitting units and
the second light emitting units.

Claims:

1. A light emitting device comprising: a board; a plurality of first
light emitting units each of which includes a first light emitting
element mounted on the board to emit light having a wavelength of 250 nm
to 500 nm and a first fluorescent layer formed on the first light
emitting element, the first fluorescent layer including a green phosphor;
a plurality of second light emitting units each of which includes a
second light emitting element mounted on the board to emit the light
having the wavelength of 250 nm to 500 nm and a second fluorescent layer
formed on the second light emitting element, the second fluorescent layer
including a red phosphor, the second fluorescent layers and the first
fluorescent layers being separated in a non-contact manner with air
interposed therebetween; and a plurality of third light emitting units
each of which includes a third light emitting element mounted on the
board to emit the light having the wavelength of 250 nm to 500 nm and a
resin layer formed on the third light emitting element, the resin layer
including neither a green phosphor nor a red phosphor, the third light
emitting units being disposed between the first light emitting units and
the second light emitting units.

2. The device according to claim 1, wherein the third light emitting
element is a blue LED.

3. The device according to claim 1, wherein the resin layer is made of a
transparent resin.

4. The device according to claim 1, wherein the resin layer is made of a
silicone resin.

5. The device according to claim 1, wherein the resin layer includes a
yellow phosphor.

6. The device according to claim 1, wherein the first, second, and third
light emitting elements are an identical kind of light emitting element.

7. The device according to claim 1, wherein the green phosphor has a
composition expressed by equation (1):
(M1-x1Eux1)3-y1Si13-z1Al3+z1O.sub.2+uN21-w
(1) (In the equation (1), M is an element selected from IA group
elements, IIA group elements, IIIA group elements, IIIB group elements
except Al (Aluminum), rare-earth elements, and IVB group elements, and
x1, y1, z1, u, and w satisfy the following relationship: 0<x1<1,
-0.1<y1<0.3, -3<z1.ltoreq.1, -3<u-w≦1.5)

8. The device according to claim 1, wherein the red phosphor has a
composition expressed by equation (2):
(M'1-x2Eux2).sub.a1Si.sub.b1AlO.sub.c1N.sub.d1 (2) (In the
equation (2), M' is an element selected from IA group elements, IIA group
elements, IIIA group elements, IIIB group elements except Al (Aluminum),
rare-earth elements, and IVB group elements, and x2, a1, b1, c1, and d1
satisfy the following relationship: 0<x2<1, 0.55<a1<0.95,
2.0<b1<3.9, 0<c1<0.6, 4<d1<5.7)

9. The device according to claim 7, wherein the red phosphor has a
composition expressed by the equation (2):
(M'1-x2Eux2).sub.a1Si1.sub.b1AlO.sub.c1N.sub.d1 (2) (In the
equation (2), M' is an element selected from IA group elements, IIA group
elements, IIIA group elements, IIIB group elements except Al (Aluminum),
rare-earth elements, and IVB group elements, and x2, a1, b1, c1, and d1
satisfy the following relationship: 0<x2.ltoreq.1,
0.55<a1<0.95, 2.0<b1<3.9, 0<c1<0.6, 4<d1<5.7)

10. The device according to claim 1, wherein the plurality of first light
emitting units, the plurality of second light emitting units, and the
plurality of third light emitting units are arrayed in column,
respectively, and the column of the third light emitting units is
disposed between the column of the first light emitting units and the
column of the second light emitting units.

11. The device according to claim 1, wherein the plurality of second
light emitting units are surrounded by the plurality of third light
emitting units, and the plurality of third light emitting units are
surrounded by the plurality of first light emitting units.

12. The device according to claim 1, wherein the plurality of first light
emitting units are surrounded by the plurality of third light emitting
units, and the plurality of third light emitting units are surrounded by
the plurality of second light emitting units.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is based upon and claims the benefit of priority
from Japanese Patent Application No. 2010-198631, filed on Sep. 6, 2010,
and No. 2011-177807, filed on Aug. 16, 2011; the entire contents of which
are incorporated herein by reference.

[0003] Recently, attention focuses on a so-called white-color Light
Emitting Device (LED) in which a yellow phosphor such as YAG:Ce is
combined with a blue LED to emit white-color light by single chip.
Conventionally, the LED emits red, green, or blue light in monochromatic
form, and it is necessary that plural LEDs emitting monochrome
wavelengths are driven in order to emit the white-color light or
intermediate-color light. However, currently the combination of the light
emitting diode and the phosphor realizes the white-color light with a
simple structure.

[0004] An LED lamp in which the light emitting diode is used is applied to
various display devices of a mobile device, a PC peripheral device, an OA
device, various switches, a light source for backlight, and a display
board. In the LED lamps, there is a strong demand for high efficiency.
Additionally, there is a demand for high color rendering in
general-purpose lighting applications, and there is a demand for high
color gamut in LCD TV backlight applications. High efficiency of the
phosphor is required for the purpose of the high efficiency of the LED
lamp, and a white-color light source in which a light source emitting
blue excitation light, a phosphor excited by blue light to emit green
light, and a phosphor excited by blue light to emit red light are
combined is preferable for the high color rendering and the high color
gamut.

[0005] The high-power LED generates heat during its operation, and
generally the phosphor is heated up to about 100 to about 200° C.
When the temperature rise is occurred, generally emission intensity of
the phosphor is degraded to cause so-called thermal quenching. Therefore,
the luminous efficiency is degraded particularly in a high-temperature
range, that is, a high-current range.

[0006] Additionally, when plural phosphors are used, the luminous
efficiency is degraded by reabsorption between phosphors. Particularly,
when the white-color light is obtained by a combination of the plural
phosphors on one LED chip, the problem becomes obvious by shortening a
distance between the phosphors.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is a schematic top view illustrating a light emitting device
according to a first embodiment;

[0015] A light emitting device according to one embodiment includes: a
board; a plurality of first light emitting units each of which includes a
first light emitting element that is mounted on the board to emit light
having a wavelength of 250 nm to 500 nm and a first fluorescent layer
that is formed on the first light emitting element, the first fluorescent
layer including a green phosphor; a plurality of second light emitting
units each of which includes a second light emitting element that is
mounted on the board to emit the light having the wavelength of 250 nm to
500 nm and a second fluorescent layer that is formed on the second light
emitting element, the second fluorescent layer including a red phosphor,
the second fluorescent layers and the first fluorescent layers being
separated in a non-contact manner with gas interposed therebetween; and a
plurality of third light emitting units each of which includes a third
light emitting element that is mounted on the board to emit the light
having the wavelength of 250 nm to 500 nm and a resin layer that is
formed on the third light emitting element, the resin layer including
neither a green phosphor nor the red phosphor, the third light emitting
units being disposed between the first light emitting units and the
second lights emitting unit.

[0016] Embodiments will be described below with reference to the drawings.

[0017] As used herein, the green phosphor means a phosphor that emits
light ranging from a blue-green color to a yellow-green color
(hereinafter also referred to as green color), that is, light having a
peak at the wavelength of 490 to 580 nm, which is longer than the
excitation light, when the phosphor is excited by light having the
wavelength of 250 nm to 500 nm, that is, near-ultraviolet light or blue
light.

[0018] As used herein, the red phosphor means a phosphor that emits light
ranging from an orange color to a red color (hereinafter also referred to
as red color), that is, light having a peak at the wavelength of 580 to
700 nm, which is longer than the excitation light, when the phosphor is
excited by the light having the wavelength of 250 nm to 500 nm, that is,
the near-ultraviolet light or the blue light.

[0019] As used herein, the yellow phosphor means a phosphor that emits
yellow light, that is, light having a peak at the wavelength of 550 to
580 nm, which is longer than the excitation light, when the phosphor is
excited by the light having the wavelength of 250 nm to 500 nm, that is,
the near-ultraviolet light or the blue light.

First Embodiment

[0020]FIG. 1 is a schematic top view illustrating a light emitting device
according to the first embodiment. FIG. 2 is a sectional view taken on a
line A-A of FIG. 1.

[0021] The light emitting device of the first embodiment is a white-color
light emitting device in which plural first light emitting units 12,
plural second light emitting units 14, and plural third light emitting
units 16 are disposed on a board 10.

[0022] The plural first light emitting units 12, the plural second light
emitting units 14, and the plural third light emitting units 16 are
arrayed in column, respectively. The column of the third light emitting
units 16 is disposed between the column of the first light emitting unit
12 and the second light emitting units 14.

[0023] The first light emitting unit 12 includes a first light emitting
element 12a that is mounted on the board and a first fluorescent layer
12b that is formed on the first light emitting element 12, and includes
the green phosphor. The second light emitting unit 14 includes a second
light emitting element 14a that is mounted on the board and a second
fluorescent layer 14b that is formed on the second light emitting element
14b, and includes the red phosphor. The third light emitting unit 16
includes a third light emitting element 16a that is mounted between the
first light emitting element 12a and the second light emitting element
14a and a transparent resin layer 16b, such as a silicone resin, which is
formed on the third light emitting element 16a.

[0024] The first light emitting element 12a, the second light emitting
element 14a, and the third light emitting element 16a emit the
near-ultraviolet light to the blue light, that is, the light having the
wavelength of 250 nm to 500 nm. In the first embodiment, the first light
emitting element 12a, the second light emitting element 14a, and the
third light emitting element 16a are described as the same kind of blue
LED chip by way of example. Desirably all the first light emitting
element 12a, the second light emitting element 14a, and the third light
emitting element 16a are the same kind of light emitting element from the
viewpoint of ease of design or production. However, the first light
emitting element 12a, the second light emitting element 14a, and the
third light emitting element 16a may be different kinds of light emitting
elements.

[0025] For example, each of the light emitting elements 12a, 14a, and 16a
is connected to wiring (not illustrated) through a gold wire 20. Driving
currents are supplied to the light emitting elements 12a, 14a, and 16a
from the outside through the wiring, whereby the light emitting elements
12a, 14a, and 16a emit the blue light for excitation.

[0026] The fluorescent layers are formed while the green phosphor and the
red phosphor are dispersed in the transparent resin, for example, a
silicone resin, respectively.

[0027] In the first embodiment, a so-called sialon phosphor is applied to
the green phosphor and the red phosphor. Because the decrease in luminous
efficiency at high temperature, that is, the thermal quenching is small
in the sialon phosphor, the sialon phosphor is suitable to the
high-density-packaging or high-power light emitting device.

[0028] The sialon green phosphor of the first embodiment has a composition
expressed by the following equation (1), and the red phosphor has a
composition expressed by the following equation (2).

(M1-x1Eux1)3-y1Si13-z1Al3+z1O.sub.2+uN21-w
(1)

[0029] (In the equation (1), M is an element that is selected from IA
group elements, IIA group elements, IIIA group elements, IIIB group
elements except Al (Aluminum), rare-earth elements, and IVB group
elements. And x1, y1, z1, u, and w satisfy the following relationship.

0<x1<1,

-0.1<y1<0.3,

-3<z1≦1,

-3<u-w≦1.5)

[0030] The sialon phosphor having the composition expressed by the
equation (1) is a green phosphor (G). The green phosphor (G) emits the
light ranging from the blue-green color to the yellow-green color, that
is, the light having the peak at the wavelength of 490 to 580 nm, which
is longer than the excitation light, when the green phosphor (G) is
excited by the light having the wavelength of 250 nm to 500 nm, that is,
the near-ultraviolet light or the blue light.

[0031] Desirably, the element M is Sr (Strontium). The element M may
include other elements such as Ca (Calcium) less than or equal to around
10 mol % in addition to Sr.

(M'1-x2Eux2).sub.a1Si.sub.b1AlO.sub.c1N.sub.d1 (2)

[0032] (In the equation (2), M' is an element that is selected from IA
group elements, IIA group elements, IIIA group elements, IIIB group
elements except Al (Aluminum), rare-earth elements, and IVB group
elements. And x2, a1, b1, c1, and d1 satisfy the following relationship.

0<x2<1,

0.55<a1<0.95,

2.0<b1<3.9,

0<c1<0.6,

4<d<5.7)

[0033] The sialon phosphor having the composition expressed by the
equation (2) is a red phosphor (R). The green phosphor (R) emits the
light ranging from the orange color to the red color, that is, the light
having the peak at the wavelength of 580 to 700 nm, which is longer than
the excitation light, when the red phosphor (R) is excited by the light
having the wavelength of 250 nm to 500 nm, that is, the near-ultraviolet
light or the blue light.

[0034] Desirably, the element M' is Sr (Strontium). The element M' may
include other elements such as Ca (Calcium) less than or equal to around
10 mol % in addition to Sr.

[0037] The first light emitting element 12a constitutes a light source
that excites the green phosphor in the first fluorescent layer 12b, and
the first light emitting unit 12 emits the green light. The second light
emitting element 14a constitutes a light source that excites the red
phosphor in the second fluorescent layer 14b, and the second light
emitting unit 14 emits the red light. The third light emitting element
16a constitutes a light source of the blue light, and the third light
emitting unit 16 emits the blue light.

[0038] The green light, the red light, and the blue light, emitted from
the first light emitting unit 12, the second light emitting unit 14, and
the third light emitting unit 16, are mixed to generate the white-color
light.

[0039] For example, when the sialon red fluorescent layer and the sialon
green fluorescent layer emit light while being stacked on one blue LED
chip without separating the sialon red fluorescent layer and the sialon
green fluorescent layer, in the order of several percent light emitted
from the green fluorescent layer is absorbed by the red fluorescent
layer, thereby degrading the luminous efficiency of the light emitting
device.

[0040] In the first embodiment, the first fluorescent layer 12a and the
second fluorescent layer 14a are separated in a non-contact manner with
gas interposed therebetween. In the first embodiment, the gas is air.
Accordingly, the first fluorescent layer 12a and the second fluorescent
layer 14a are separated without interposing a solid-state layer, such as
resin, which causes scattering and diffusion. Therefore, a ratio of the
green light from the green fluorescent layer reaching the red fluorescent
layer and a ratio of the red light from the red fluorescent layer
reaching the green fluorescent layer are decreased to suppress the
reabsorption. Particularly, the reabsorption of the green light by the
red phosphor having the high absorption factor of the green emission
region is effectively suppressed.

[0041] The third light emitting unit 16 is disposed between the first
light emitting unit 12 and the second light emitting unit 14. Therefore,
a distance between the first fluorescent layer 12a and the second
fluorescent layer 14a is further increased. Accordingly, the reabsorption
can further be suppressed. Because the third light emitting unit 16 is
disposed in the gap between the first fluorescent layer 12a and the
second fluorescent layer 14a, the packaging density of the white-color
light emitting device is not decreased.

[0042] According to the first embodiment, the white-color light emitting
device that suppresses the reabsorption between the phosphors with the
high packaging density to realize the excellent luminous efficiency can
be provided with simple configuration.

Second Embodiment

[0043] A second embodiment differs from the first embodiment in that the
third light emitting elements are mounted between all the first light
emitting elements and all the second light emitting elements, that is,
the third light emitting units are disposed between all the first light
emitting units and all the second light emitting units. Therefore, the
descriptions of the contents overlapped with those of the first
embodiment are omitted.

[0044]FIG. 3 is a schematic top view illustrating a light emitting device
of the second embodiment. Because the third light emitting elements are
mounted between all the first light emitting elements and all the second
light emitting elements, the third light emitting units 16 are disposed
between all the first light emitting units 12 and all the second light
emitting units 14.

[0045] According to the second embodiment, all the distances between the
first fluorescent layers 12a and the second fluorescent layers 14a are
increased. Accordingly, the reabsorption can further be suppressed.
Because the third light emitting units 16 that emit the blue light are
disposed in the gaps between the first fluorescent layers 12a and the
second fluorescent layers 14a, the packaging density of the white-color
light emitting device is not decreased.

Third Embodiment

[0046] A third embodiment differs from the second embodiment in that the
plural second light emitting units are surrounded by the plural third
light emitting units, and the plural third light emitting units are
surrounded by the first light emitting units. Therefore, the descriptions
of the contents overlapped with those of the second embodiment are
omitted.

[0047]FIG. 4 is a schematic top view illustrating a light emitting device
of the third embodiment. The second light emitting units 14 are disposed
near the center of the board 10. A periphery of the second light emitting
units 14 is surrounded by the third light emitting units 16. A periphery
of the third light emitting units 16 is surrounded by the first light
emitting units 12.

[0048] Therefore, the third light emitting units 16 are disposed between
all the first light emitting units 12 and all the second light emitting
unit 14.

[0049] According to the third embodiment, similarly to the second
embodiment, all the distances between the first fluorescent layers 12a
and the second fluorescent layers 14a are increased. Accordingly, the
reabsorption can further be suppressed. Because the third light emitting
units 16 that emit the blue light are disposed in the gap between the
first fluorescent layers 12a and the second fluorescent layers 14a, the
packaging density of the white-color light emitting device is not
decreased. Advantageously the production is facilitated.

[0050] Alternatively, the plural first light emitting units may be
surrounded by the plural third light emitting units, and the plural third
light emitting units may be surrounded by the plural second light
emitting units.

[0051] While certain embodiments have been described, these embodiments
have been presented by way of example only, and are not intended to limit
the scope of the inventions. Indeed, the light emitting device described
herein may be embodied in a variety of other forms; furthermore, various
omissions, substitutions and changes in the form of the devices and
methods described herein may be made without departing from the spirit of
the inventions. The accompanying claims and their equivalents are
intended to cover such forms or modifications as would fall within the
scope and spirit of the inventions.

[0052] For example, in addition to the blue LED chip, a semiconductor
light emitting element that emits the light in the ultraviolet region or
the blue light may be used as the light emitting element that emits the
excitation light used in the light emitting device. For example, a
gallium nitride compound semiconductor can be used as the LED. However,
when the semiconductor light emitting element that emits the ultraviolet
light is used as the excitation light source, it is necessary that a
filter mechanism that blocks the ultraviolet light be provided in the
light emitting device.

[0053] In the embodiments, the transparent resin layer is directly formed
on the blue LED chip by way of example. Alternatively, for example, the
transparent resin layer may be provided between the blue LED chip and the
fluorescent layer or in an outer surface of the fluorescent layer.

[0054] In the embodiments, the sialon phosphor is applied to the green
phosphor and the red phosphor by way of example. From the viewpoint of
suppressing the thermal quenching, the sialon fluorescent, particularly
the phosphors expressed by the equations (1) and (2) are desirably
applied. Alternatively, another phosphor may be applied.

[0055] In the embodiments, for example, phosphors having plural
compositions may be used as the first or second fluorescent layer in
order to adjust color development of the light emitting device or
white-color LED. The fluorescent layer may be formed by mixing the plural
phosphors, or the fluorescent layer may be formed by stacking plural
fluorescent layers including different phosphors.

[0056] The disposition patterns of the first to third light emitting
element are not limited to the embodiments. However, any pattern can be
adopted as long as the third light emitting element is mounted between
the first and second light emitting elements.

[0057] In the embodiments, the silicone transparent resin is used as the
resin layer formed on the third light emitting element by way of example.
Alternatively, another transparent resin may be applied. The fluorescent
layer including the yellow phosphor may be used as the resin layer in
order to adjust the emission color of the light emitting device.